1. Field of the Invention
This invention relates to a boot or seal for a power transmitting mechanical joint, especially for a joint which is subject to articulation during operation. More particularly, this invention relates to a boot or seal of the aforesaid type in which at least a portion of such boot is of a semi-rigid character. Specifically, this invention relates to a boot or seal for a constant velocity joint of the type used in driving a front wheel of a front wheel drive automotive vehicle, in which the portion of the seal or boot which surrounds the outer race of the joint is made up of concentric separate inner and outer components, each of which is of semi-rigid character.
2. Description of the Prior Art
Constant velocity drive joints are widely used in the automotive industry as means to transmit power from the transmission of a front wheel drive vehicle to the driven front wheels of the vehicle, with one or more of such joints being provided for each of the driven wheels. Each such drive joint must be sealed, of course, to maintain the necessary lubrication in place within the joint and to keep the joint free from contamination by dirt and other external contaminants.
The devices heretofore used to accomplish this sealing function, which are usually referred to as seals or boots, have usually been of a flexible construction, usually constructed of an elastomeric material and usually in a pleated configuration. Such flexible construction, however derived, gives the boot the ability to distort to accommodate articulation or angular movement of the normally axially aligned input and output shafts of the joint, an operational condition which can develop due to road vibration or cornering, for example, without breaking the seal of the joint during such articulation.
Flexible boots or seals for automotive constant velocity drive joints, as heretofore described, have been utilized quite extensively. However, these seals are quite expensive, and due to the fact that their dimensions readily change by virtue of their flexible nature, they must be installed using manual operations, which precludes the use of some cost-saving mechanical assembly techniques that rely on precise dimensions of the part being installed. Additionally, these flexible boots or seals, which are made from elastomeric materials, are subject to puncture in use due to road hazards and other forms of concentrated impacts, and these materials are known to be subject to degradation of properties when exposed to low temperatures or high temperatures of the type that can be encountered during the normal life of an automobile. Additionally, due to the pleated configuration of these flexible boots or seals, the interior volume, which must be filled with grease to properly lubricate the associated joint, requires a rather large volume of grease for that purpose. Furthermore, many elastomeric materials are subject to degradation when exposed to grease, and the grease sensitivity further limits the useful life of such flexible seals.
The aforesaid co-pending U.S. Pat. application Ser. No. 702,051 describes a boot or seal for a mechanical joint that has a non-flexible organic portion with a part-spherical inner surface that articulatingly seals on the part-spherical outer surface of the outer race of the universal joint, which outer race is usually metallic. The non-flexible organic first portion is of integral construction and has a part-spherical slot therein which sealingly receives a second portion which articulates in such slot.
In the embodiment of FIG. 1 of the aforesaid co-pending U.S. Pat. application Ser. No. 702,051, the non-flexible organic portion of the boot or seal of the mechanical joint depicted therein is integrally formed, which leads to uniform hardness and other properties throughout such non-flexible organic portion of the boot or seal. However, it has now been discovered that the performance of the non-flexible organic portion of the boot or seal of the mechanical joint depicted in FIG. 1 of the aforesaid co-pending U.S. Pat. application Ser. No. 702,051 can be improved by constructing such portion from at least a pair of non-flexible organic portions, components, or segments, each of which is selected from a slightly different non-flexible organic material to provide differing hardness and other properties in each such component to optimize the performance of each such components in the mechanical joint in which it is used.